1. Field of the Invention
This invention relates to "block copolymers" suitable for use in organic fluid compositions. In particular, this invention relates to block copolymers composed of at least two blocks, fluid compositions containing the same and the processes of preparing copolymers.
2. Description of the Prior Art
U.S. Pat. No. 3,050,511 describes block copolymers obtained from polystyrene and alkylene oxide. The technique involves forming a "living polymer" of the styrene in the presence of an anionic catalyst, then adding the alkylene oxide to it. Such products, however, would not be suitable as hydrocarbon fluid additives because they have insufficient solubility in lubricating oils to retain their effectiveness and they lack suitable terminal groups for thermal and oxidative stability. U.S. Pat. No. 3,219,725 describes a block polymer of oxymethylene and styrene or alpha-methylstyrene by polymerizing styrene and adding formaldehyde to produce a polyoxymethylene block. It is understood that the resulting block copolymer may be terminated by esterification. Olefin oxide, higher aldehydes, isocyanates and the like may replace the styrene. Again, the use of styrene polymer as the first block-forming monomer or replacement by a polar monomer would not produce a useful multifunctional additive for lubricating oils. U.S. Pat. No. 3,281,499 describes block copolymers of oxymethylene and olefins, such as styrene. The resulting products are moldable polymers which are of little solubility in lubricating oils or other organic fluids. U.S. Pat. No. 3,318,813 describes a tert-butylstyrene polymer prepared in an anionic polymerization using n-butyl lithium as the initiator. Polymerization is terminated in methanol. This polymer is said to be useful as a viscosity index (VI) improver. The polymers used in this reference contain no polar groups. Hence, these homopolymers are distinguishable from the copolymers of the present invention. U.S. Pat. No. 3,175,997 claims a process of preparing terminally reactive polymers, such as butadiene-styrene copolymers, by reacting with ethylene oxide and acidifying the alkali metal group to --OH. The products are used in adhesives, potting compounds and binders. U.S. Pat. No. 2,835,658 describes treating styrene-lactone block polymers with diisocyanates. The polymers are elastomers prepared from free-radical bulk polymerization. G. B. Pat. No. 1,304,289 describes hydrogenated butadiene-styrene copolymers as VI improvers. These polymers contain no polar polymer blocks. U.S. Pat. No. 3,867,295 describes block copolymers of the AB or BAB type prepared from alkylstyrene of hydrogenated butadienestyrene and alkylene oxide or sulfide. These products have utility in lubricating oil compositions as VI improvers or detergents.